This invention relates generally to measuring appearance variations in molded plastic parts, and specifically to tools for duplicating the streaking seen in real parts and measurement and analysis of the streaking.
Consumers of durable plastic products including, for example, toys, computer and printer housings, and vehicles expect a uniform surface finish with no visible flaws, streaks, or defects. Common defects include streaks where various plastic flows meet in a part. These streaks may arise as different flow fronts from different gates meet or downstream of flow disruptions such as grills, bosses, ribs, or holes.
Currently, few, if any, numerical specifications related to uniformity of appearance are given to a supplier of raw plastic products outside of average color and possibly gloss or haze. Nevertheless, the molder creating the part and the consumer each expect a product with no visible flaws. The consumer, in particular, may view appearance defects as both unsightly and as indicative of poor quality material.
Currently, the quality, uniformity, and lack of defects in a part is typically judged using visual inspection on production parts. This leads to an absence of numerical specifications, lack of consistency due to operator variation, and an inability to consistently and rapidly process a large number of samples. Further, a large amount of waste may be generated since a large number of defective parts must be molded to attempt to quantify the problem. Often, the molder or customer is unable to transmit a complaint to the plastic supplier that is more specific than “a streaking problem exists,” and many pounds of rejected production parts are shipped back to the plastic supplier for subsequent visual evaluation. Yet, it is difficult for the supplier to address the problem and provide solutions in the absence of effective measurement tools.
Several prior commonly-assigned and invented patents and patent applications, namely, U.S. Pat. No. 5,859,708, issued Jan. 12, 1999; and application Ser. Nos. 09/075,913; 09/188,094; and 09/188,095; address vagaries of visual inspection via a spatially resolved spectrometer which can resolve small defects that are not apparent to a standard spectrometer with the typical ½ inch diameter or larger aperture. Further, unlike the few spectrometers capable of smaller apertures that are not automated, the spectrometer described earlier may be interfaced with a computer for motorized sample movement and automatic data collection.
However, several problems remain. First, complex, curved, or textured parts are not amenable to automated inspection. Second, this spatially resolved spectrometer generates massive amount of data and automated data reduction is necessary to screen parts.
Accordingly, there is a need in the art for and improved system and method to quantify appearance defects in molded plastic parts,